Metallic core for electromagnets



Patented Jan. 5, 1932 ERNST HOCHHEIM, OF HEIDELBERG, GERMANY, ASSIGNOR TO I. G. FARBENIND'USTRIE AKTIENGESELLSCHAFT, OF FRANKFORT-ON-THE-MAIN, GERMANY, A. CORPORATION OF GERMANY METALLIC CORE FOR ELECTROMAGNE'IS No Drawing. Application filed August 13, 1926, Serial No. 129,093, and in Germany August 19, 1925.

I have found that it is of great advantage to make metallic cores for electro-magnets, transformers and the like which are to be operated both with rapid and slow oscillations, but do not choke such oscillations, of metallic powders in a state of extremely fine sub-division which are obtained by the thermal decomposition of metal carbonyls. F or example the metal carbonyls are decomposed by contact with heated solid bodies or in hot liquids or melts, or the carbonyl vapors are introduced into a heated vessel and decomposed substantially in the free space thereof and not by contact with the hot walls in the manner described and the fine powdery metal is separated in dust collecting chambers or by any other suitable means. In case the temperature at which the decomposition of the metal carbonyl is effected, is rather low, it is often advantageous to heat the resulting metallic powder for some time in an atmos-. phere of inert gas.

The cores according to the present invention are prepared from the powdery metals by pressing, preferably with the employment of very high pressures up to 20,000 kilograms per square centimetre. If desired, the metal powder is mixed with small amounts of a inding or adhesive substance such as an alcoholic solution of shellac, before pressing.

The cores prepared according to my present invention from metallic powders obtained by decomposition of metal carbonyls are greatly superior in their properties to cores prepared in a similar manner from the powdery metals hitherto marketed. For example when employed in the form of rings, they show a very small eddy-current loss, a very small alteration of the inductivity and a resistance causing losses depending only slightly and nearly proportionally on the frequency of the oscillations. The cores according to this invention are especially suitable for use in so-called Pupin coils and small transformers for example for the purpose of wireless telegraphy or telephony or any other apparatus working with both slow and rapid electric oscillations.

The powdery metals hitherto employed for the manufacture of cores generally contain impurities which unfavorably influence the hysteretic losses in energy. The metal powders obtained from carbonyls are completely free from hydrogen, sulfur, phosporous, silicon and metals not capable of forming carbonyls. Further, in the powders hitherto in use, the grains have generally the size of about 0.001 millimetre, while by the decomposition of carbonyls the powders may be obtained with much smaller grains, for example of 0.00001 millimetre in size. F or insulating the grains it was hitherto necessary to subject the powdery metal to oxidation which often cannot be uniformly effected, or to admix insulating materials before the pressing operation, whereby the permeability was kept rather small. In the metal powders prepared from carbonyls, each grain is coated with a thin superficial layer of metal oxid which is formed in the preparation. Therefore, any subsequent oxidation or the addition of glass, porcelain or other insulating material which would unfavorably influence the density and permeability of the core, may be dispensed with. For these reasons the hysteretic losses are very small and nearly all constants depend only very slightly on the frequency, when working with cores according to the present invention; therefore the said cores are especially suitable for use with very rapid electric oscillations.

When for example a bar-shaped core prepared according to this invention is introduced into a weakly coupled coil of an oscillation circuit, no alteration of the wave length and no dependency of the self-induction on the frequency occurs, so that in this respect the core behaves as air; on the other hand the core allows of an energy being taken up in the case of resonance, which is nearly thrice as great as with other materials.

In most cases, the cores according to my present invention will be made of iron powder obtained by the thermal decomposition of iron carbonyl. However, it may also be advantageous to employ powdery nickel or cobalt or mixtures of several such metals, for example iron-nickel or iron-cobalt, which mixtures may be obtained by subjecting a mixture of two or more metal carbonyls to, thermal decomposition. What I claim is:

1. Cores for electro-ma ets, transformers 5 and other electro-ma et1c apparatus comprising pressed pow ery iron obtained by thermal decomposition of iron carbonyl.

2. Cores for electro-magnets, transformers and other electro-magnetic apparatus com risin a prepared powdery metal selected rom t e class consisting of iron, nickel and cobalt obtained by thermal decomposition of the corresponding carbonyl.

In testimony whereof I have hereunto set my hand.

ERNST HOCHHEIM. 

